This invention relates to a character image data compression system for compressing binary data from an image matrix corresponding to a two-dimensional character image, and particularly, provides a character image data compression system suitable for Chinese characters (hereinbelow called "Kanji" etc. in which, in a case where a character image segment occurs in adjacent lines (hereinafter called "previous line" and present line"), mutual "contact modes" in a row direction (normal to a line direction) of the character image segments in two sequential lines are discriminated and coded data relating to different types of information is outputted incidentally to a control code prescribing the contact modes. The term "contact mode" is used herein to mean the spatial relationship between the part of the character image appearing in the previous line, and the part in the present line.
FIG. 1 shows one example of bit data (binary data) of Chinese character " " which is used in relatively high frequency as "kanji" and obtained by a raster scanning method in which a line direction is considered to be main scanning direction, the example being shown as typical bit explosion in matrix.
As is apparent from FIG. 1, the "kanji" is far complicatedly composed of a large number of line or curve ports in comparison with an alpha-numeric language (European language; numeral), and in view of character image segments in the bit data of the respective line directions, fork and joint phenomena are frequently recognized in some portions every time when the line changes, for example, in FIG. 1, the segments A and B join to the segment C and the segment D forks into the segments E, F, and G.
Conventionally, a so-called run-length method are well known and a two-dimensional difference method as compression techniques of character image data and also known are methods which have improvements over the aforementioned methods. However, these conventional methods do not consider at all the characteristics of the "kanji" or take less consideration thereof, so that it will be said that these conventional methods are necessarily suitable for a compression method of "kanji" data.
Moreover, with respect to the "kanji", it is necessary to always keep 2,000 to 3,000 types of characters per one font which are used with relatively high frequency and, in a photocomposing technique, 10,000 to 12,000 types of characters per one font which are used with relatively low frequency, so that data compression ratio affects significantly the saving in capacity for a memory of the character image data. For example, in a case where one character is analyzed into a matrix of 400.times.400 image elements total data in the case of 10,000 character types before compression includes 400.times.400.times.10,000 (bits)=200 (megabytes), and accordingly, the improvement of 1 point of the data compression ratio results in saving the memory 2 megabytes and results in cost reduction.